This is the crux of it, and not enough emphasis is placed on this. It is the unprecedented rate of warming more than the total amount that is of greatest concern if you've studied any paleoclimatology and seen how long it takes for natural systems to re-establish in a new climate regime.

There has been a lot of study on how the transition to the current interglacial climate affected the biogeography, and you can see how forests, coral reefs, etc. were still trying to relocate several thousands of years into it. Now, of course, they're screwed, and we have mass forest fires and the like because they have no hope of adapting anymore.